1. Field of the Invention
The present invention relates to a thermosetting resin composition, and a prepreg and a laminated sheet for electrically insulating material using the thermosetting resin composition.
2. Prior Art
As printed wiring boards for electronic appliance, laminated sheets mainly using an epoxy resin have been widely used. However, in accordance with tendencies that a pattern becomes finer due to the increase in the mounting density in electronic appliance, the surface mount system is generally employed, the signal propagation velocity becomes higher, and the frequency of the signal used becomes higher, a development of printed wiring board materials having a low dielectric loss and an improved heat resistance are strongly desired.
As a prior art of a resin composition or laminated sheet using an epoxy resin as a curing agent and using a copolymer resin comprising styrene and maleic anhydride, for example, Japanese Unexamined Patent Publication No. 109476/1974 has a description about a flexible printed wiring board from a flexible epoxy resin and a copolymer resin which comprises styrene and maleic anhydride, wherein a reactive epoxy diluent and an acrylonitrile-butadiene copolymer are necessary for imparting flexibility to the printed wiring board. In addition, Japanese Unexamined Patent Publication No. 221413/1989 has descriptions about a copolymer resin having an acid value of 280 or more, which is obtained from an epoxy resin, an aromatic vinyl compound, and maleic anhydride, and about an epoxy resin compound containing dicyanamide. Further, Japanese Unexamined Patent Publication No. 25349/1997 has descriptions about a prepreg and a laminated sheet material for electrical appliance, comprising a brominated epoxy resin, a copolymer resin comprising styrene and maleic anhydride (epoxy resin curing agent), a styrene compound, and a solvent. Japanese Unexamined Patent Publications No. 17685/1998 and No. 17686/1998 have descriptions about a prepreg and a laminated sheet material for electrical appliance, comprising an epoxy resin, a copolymer resin of an aromatic vinyl compound and maleic anhydride, and a phenolic compound. Japanese Unexamined national Patent Publication (kohyo) No. 505376/1998 has descriptions about a resin composition, a laminated sheet, and a printed wiring board, comprising an epoxy resin, a cross-linking agent for carboxylic anhydride-type epoxy resin, and an allyl network-forming compound. However, these prior art materials do not have performance required for the tendency that the pattern becomes finer and the frequency of the signal becomes higher, that is, they do not have low dielectric loss, excellent heat resistance, excellent moisture resistance, and excellent adhesion to a copper foil.
It is an object of the present invention to provide a thermosetting rein composition free of the above-stated problems, which composition is excellent in all, low dielectric loss, heat resistance, moisture resistance, and adhesion to a copper foil, and the use thereof, for example, a prepreg and a laminated sheet.
In one aspect, the present invention is directed to a thermosetting resin composition comprising:
(1) a copolymer resin comprising (a) a monomer unit represented by the following general formula (I): 
wherein R1 represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 5 carbon atoms; R2 or each of R2""s independently represents a halogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, or an aromatic hydrocarbon group; x is an integer of 0 to 3, preferably 0; and m is a natural number, and
(b) a monomer unit represented by the following general formula (II): 
wherein n is a natural number; and
(2) a thermosetting resin which is cured together with said component (1),
wherein a cured product of said composition has a dielectric constant of 3.0 or less at a frequency of 1 GHz or more and has a glass transition temperature of 170xc2x0 C. or more, and the composition is not constituted only by said (1).
In one aspect of the present invention, it is preferred to use a thermosetting resin composition wherein the said component (1) is replaced by (1)xe2x80x2 a copolymer resin comprising the said monomer unit (a) and (b), and further comprises, as a monomer unit (c), N-phenylmaleimide represented by the following general formula (III): 
wherein R3 represents a halogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group, a hydroxyl group, a thiol group, or a carboxyl group; y is an integer of 0 to 3, preferably 0; and r is a natural number,
and/or a derivative thereof. In addition, it is also preferred that the component (2) a thermosetting resin is (2)xe2x80x2 a cyanate resin having at least two cyanate groups per molecule.
In another aspect, the present invention is directed to a thermosetting resin composition comprising:
(1) a copolymer resin comprising
(a) a monomer unit represented by the following general formula (I): 
wherein R1 represents a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 5 carbon atoms; R2 or each of R2""s independently represents a halogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group, or a hydroxyl group; x is an integer of 0 to 3, preferably 0; and m is a natural number, and
(b) a monomer unit represented by the following general formula (II): 
wherein n is a natural number; and
(2)xe2x80x2 a cyanate resin having at least two cyanate groups per molecule.
In another aspect of the present invention, it is preferred to use a thermosetting resin composition wherein the said component (1) is replaced by (1)xe2x80x2 a copolymer resin comprising the said monomer unit (a) and (b), and further comprises, as a monomer unit (c), N-phenylmaleimide represented by the following general formula (III): 
wherein R3 represents a halogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group, a hydroxyl group, a thiol group, or a carboxyl group; y is an integer of 0 to 3, preferably 0; and r is a natural number and/or a derivative thereof.
Hereinafter, the present invention will be described in more detail.
In the present invention, component (1) or (1)xe2x80x2 is a copolymer resin comprising styrene and maleic anhydride. In the present invention, the monomer unit (a) is obtained from a compound, such as styrene, 1-methylstyrene, vinyltoluene, dimethylstyrene, chlorostyrene, or bromostyrene, and these compounds can be used individually or in combination. Further, various polymerizable components other than the above-stated monomer units may be copolymerized, and examples of these polymerizable components include vinyl compounds, such as ethylene, propylene, butadiene, isobutylene, acrylonitrile, vinyl chloride, and fluoroethylene, and compounds having a methacryloyl group or an acryloyl group, such as methacrylate such as methyl methacrylate, and acrylate such as methyl acrylate. A substituent, such as an allyl group, a methacryloyl group, an acryloyl group, or a hydroxyl group, can be optionally introduced into the component (a) through a Friedel-Crafts reaction or a reaction using a metal catalyst, such as lithium.
In the present invention, various hydroxyl group-containing compounds, amino group-containing compounds, cyanate group-containing compounds, and epoxy group-containing compounds can be introduced into the monomer unit (b).
In the present invention, as the monomer units (c), preferred are N-phenylmaleimide and derivatives of N-phenylmaleimide, which have a phenolic hydroxyl group, from the viewpoint of obtaining excellent dielectric property and an appropriate glass transition temperature, and especially preferred is N-phenylmaleimide from the viewpoint of obtaining excellent heat resistance and excellent moisture resistance. Examples of derivatives of N-phenylmaleimide include compounds represented by general formulae (IV) to (IX): 
wherein w or each of w""s independently represents an integer of 1 to 3.
In the present invention, it is preferred that the component (1) is a copolymer resin represented by the following general formula (X): 
wherein R1, R2, m, n and x have the same meanings as stated above. The examples of R1 includes a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 5 carbon atoms, preferably a hydrogen atom or a methyl group. The examples of R2 or each of R2""s include a halogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group including a group which forms a naphthalene together with the benzene entity of the monomer (a), or a hydroxyl, preferably a hydrogen atom or a methyl group.
In the present invention, it is preferred that the component (1) is a copolymer resin represented by the following general formula (XI): 
wherein R1, m and n have the same meanings as stated above.
In the present invention, from the viewpoint of achieving a good balance of a dielectric constant and a dielectric dissipation factor with a glass transition temperature, resistance to soldering heat, and adhesion to a copper foil, it is preferred that m/n indicating the copolymerization ratio for component (1) is 0.8 to 19.
In the present invention, it is preferred that the component (1)xe2x80x2 is a copolymer resin represented by the following general formula (XII): 
wherein R1, R2, R3, m, n, r, x and y have the same meanings as stated above. The examples of R3 includes a halogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group including a group which forms a naphthalene together with the benzene entity of the monomer (c), a hydroxyl group, a thiol group, or a carboxyl group, preferably a hydrogen atom or a methyl group.
In the present invention, it is more preferred that component (1)xe2x80x2 is a copolymer resin represented by the following general formula (XIII): 
wherein R1, m, n and r have the same meanings as stated above.
In the present invention, from the viewpoint of achieving a good balance of a dielectric constant and a dielectric dissipation factor with a glass transition temperature, resistance to soldering heat, and adhesion to a copper foil, it is preferred that m/(n+r) indicating the copolymerization ratio for the component (1)xe2x80x2 is 0.8 to 19, and it is more preferred that the ratio is from 1 to 3.
In the present invention, from the viewpoint of achieving a good balance of a dielectric constant and a dielectric dissipation factor with a glass transition temperature, resistance to soldering heat, and adhesion to a copper foil, it is preferred that n/r indicating the copolymerization ratio for the component (1)xe2x80x2 is 1/49 to 49, and it is more preferred that the ratio is from 1/9 to 9.
In addition, from the viewpoint of achieving a good balance of heat resistance and a mechanical strength with formability at 200xc2x0 C. or lower, it is preferred that the weight average molecular weight of the component (1) or (1)xe2x80x2 is 1,000 to 300,000. The weight average molecular weight is measured by gel permeation chromatography using tetrahydrofuran as a solvent, in which a standard polystyrene is used for molecular weight calibration.
In the present invention, a resin cured product, which comprises the component (1) or (1)xe2x80x2 and a thermosetting resin, has preferably a dielectric constant of 3.0 or less at a frequency of 1 GHz or more and has a glass transition temperature of 170xc2x0 C. or more. From the viewpoint of achieving a good balance of low dielectric loss with heat resistance and moisture resistance, the dielectric constant is more preferably 2.2 to 3.0, especially preferably 2.4 to 2.9. From the viewpoint of achieving a good balance of heat resistance with incorporation of a resin component, moisture resistance, and low dielectric loss, the glass transition temperature is more preferably 170 to 230xc2x0 C., especially preferably 175 to 220xc2x0 C.
For obtaining a resin cured product containing the above copolymer resin, which has a dielectric constant adjusted to be 3.0 or less and has a glass transition temperature of 170xc2x0 C. or more, the resin composition of the present invention contains, in addition to the component (1) or (1)xe2x80x2, a thermosetting resin component which is cured together with the copolymer resin. As such a component, a resin having a low dielectric constant and a high glass transition temperature, which is cured together with the copolymer resin, can be used, and, by combining this resin with the component (1) or (1)xe2x80x2 in the present invention, a composition having a dielectric constant of 3.0 or less and having a glass transition temperature of 170xc2x0 C. or more can be obtained.
In the present invention, there is no particular limitation with respect to (2) a thermosetting resin provided that the resin achieves the object of the present invention. Examples of the thermosetting resin include a cyanate resin having two or more cyanate groups per molecule.
In an example of the present invention, specific examples of cyanate compounds for (2)xe2x80x2 a cyanate resin include 2,2-di(cyanatephenyl)propane, di(4-cyanate-3,5-dimethylphenyl)methane, di(4-cyanatephenyl)thioether, 2,2-di(4-cyanatephenyl)hexafluoropropane, di(cyanatephenyl)ethane, and a cyanate and a phenolic novolak cyanate of a copolymer of phenol and dicyclopentadiene, and these compounds can be used individually or in combination. Of these, more preferred is 2,2-di(cyanatephenyl)propane from the viewpoint of obtaining excellent dielectric property and excellent heat resistance, further preferred is a compound containing a mixture of a trimer and a larger oligomer (polymer) having a triazine ring preliminarily formed by self-polymerization, and, from the viewpoint of achieving a good balance of a dielectric constant and a dielectric dissipation factor with heat resistance and prevention of gelation, especially preferred is a compound in which 10 to 90 mol % of 2,2-di(cyanatephenyl)propane forms a trimer and/or a larger oligomer (polymer).
When a trimer and/or a larger oligomer (polymer) having a triazine ring is formed by self-polymerization, it is effective that a cyanate resin is preliminarily mixed with the component (1) and dissolved to form a semi-interpenetrating polymer network (semi-IPN) structure between the component (1) and a trimer and/or a larger polymer having a triazine ring derived from the cyanate resin, and, by virtue of having the semi-IPN structure, the resin composition can be improved in glass transition temperature, adhesion to a copper foil, and dielectric property.
Examples of curing catalysts for (2)xe2x80x2 the cyanate resin include organometal catalysts, such as zinc naphthenate, manganese naphthenate, and titanium naphthenate, and examples of curing accelerators include monohydric phenolic compounds, such as phenol, nonylphenol, and para-cumylphenol, and polyhydric phenolic compounds, such as bisphenol A and phenol novolak resins. Among these curing catalysts, preferred are zinc naphthenate and manganese naphthenate from the viewpoint of obtaining excellent dielectric property and excellent heat resistance, and especially preferred is zinc naphthenate from the viewpoint of obtaining a high reaction rate of the heat curing reaction. It is preferred that the amount of the curing catalyst used is 0.01 to 1.00% by weight, based on the weight of the cyanate resin from view point of achieving a good balance of a high reaction rate of the heat curing reaction, excellent dielectric property and excellent heat resistance with occurrence of gelation during the synthesis and lack of stability in resultant varnish. As the curing accelerator, monohydric phenolic compounds are preferred from the viewpoint of obtaining excellent heat resistance, and especially preferred is para-cumylphenol from the viewpoint of obtaining excellent dielectric property and excellent heat resistance. It is preferred that the amount of the curing accelerator used is 0.01 to 1.00, in terms of the ratio of the equivalent amount of phenolic hydroxyl group to the equivalent amount of cyanate group in the cyanate resin.
From the viewpoint of achieving a good balance between a glass transition temperature, resistance to soldering heat, adhesion to a copper foil, a dielectric constant, and a dielectric dissipation factor, the thermosetting resin composition of the present invention preferably comprises 10 to 300 parts by weight of component (2), more preferably comprises 50 to 300 parts by weight of the component (2), especially preferably comprises 50 to 250 parts by weight of the component (2) per 100 parts by weight of component (1) or (1)xe2x80x2.
In the present invention, as component (3), well known epoxy resins, curing agents for epoxy resins, curing accelerators for epoxy resins, isocyanurate compounds and curing catalysts therefore, thermoplastic resins, elastomers, flame retardants, and filler can be optionally used individually or in combination.
In the present invention, it is preferred that an epoxy resin of the component (3) is used as a modifier. By adding the epoxy resin to the composition, the resultant resin composition is improved in moisture resistance and heat resistance, especially in heat resistance after absorbing water. The epoxy resin can be added to the resin composition in an amount of 0 to 300 parts by weight, relative to 100 parts by weight of the component (1). With respect to the component (3), there is no particular limitation as long as it is an epoxy resin having two or more epoxy groups per molecule, and examples include bisphenol A glycidyl ether, bisphenol F glycidyl ether, biphenyl glycidyl ether, novolak glycidyl ether, multifunctional phenolic glycidyl ether, naphthalene glycidyl ether, alicyclic glycidyl ether, alcohol glycidyl ether, and halides of these glycidyl ethers, glycidyl amines, and glycidyl esters, and these can be used individually or in combination. Of these, from the viewpoint of obtaining excellent dielectric property and excellent heat resistance, preferred are dicyclopentadiene-type epoxy resins, bisphenol A novolak-type epoxy resins, biphenyl-type epoxy resins, tetrabromobisphenol A-type epoxy resins, and polydimethylsiloxane-containing epoxy resins, and especially preferred are dicyclopentadiene-type epoxy resins, biphenyl-type epoxy resins, and bisphenol A novolak-type epoxy resins from the viewpoint of obtaining excellent moisture resistance and excellent adhesion to a copper foil.
In the present invention, examples of curing agents for epoxy resins include acid anhydrides, amine compounds, and phenolic-compounds. Examples of curing accelerators for epoxy resins include imidazoles and derivatives thereof, tertiary amines, and quaternary ammonium salts.
In the present invention, examples of isocyanurate compounds include triallyl isocyanurate, trimetaallyl isocyanurate, diallylmonoglycidyl isocyanurate, monoallyldiglycidyl isocyanurate, triacryloylethyl isocyanurate, and trimethacryloylethyl isocyanurate. Of these, from the viewpoint of achieving low-temperature curing property, preferred are triallyl isocyanurate and triacryloylethyl isocyanurate. From the viewpoint of obtaining excellent dielectric property, especially preferred is triallyl isocyanurate. Examples of curing catalysts include organic peroxides, such as benzoyl peroxide and 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexene-3, which are radical initiators.
In the present invention, examples of thermoplastic resins include polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polyphenylene ether reins, phenoxy resins, polycarbonate resins, polyester resins, polyamide resins, polyimide resins, xylene resins, petroleum resins, and silicone resins.
In the present invention, examples of elastomers include polybutadiene, polyacrylonitrile, epoxy-modified polybutadiene, maleic anhydride-modified polybutadiene, phenol-modified polybutadiene, and carboxy-modified polyacrylonitrile.
In the present invention, examples of flame retardants include halogen flame retardants, such as hexabromobenzene, brominated polycarbonate, brominated epoxy resins, and brominated phenolic resins; phosphate flame retardants, such as tricresyl phosphate and tris(dichloropropyl) phosphate; and inorganic flame retardants, such as red phosphorus, antimony trioxdie, aluminum hydroxide, and magnesium hydroxide.
In the present invention, examples of the filler include inorganic substance powder, such as silica, mica, talc, glass short fiber or fine powder, and hollow glass, and organic substance powder, such as silicone powder, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, and polyphenylene ether.
In the present invention, an organic solvent can be optionally used, and there is no particular limitation with respect to the organic solvent. Examples of organic solvents include ketone solvents, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol solvents, such as ethylene glycol monomethyl ether; ether solvents, such as tetrahydrofuran; aromatic solvents, such as toluene, xylene, and mesitylene; dimethylformamide; dimethylacetamide; and N-methylpyrrolidone, and these organic solvents can be used individually or in combination.
In the present invention, an ultraviolet absorber, an antioxidant, a photopolymerization initiator, a fluorescent brightener, and an adhesion improving agent can be optionally added to the resin composition, and there is no particular limitation with respect to these additives. Examples of ultraviolet absorbers include benzotriazoles; examples of antioxidants include hindered phenol and styrenated phenol; examples of photopolymerization initiators include benzophenones, benzylketals, and thioxanthone; examples of fluorescent brighteners include stilbene derivatives; and examples of adhesion improving agents include urea compounds, such as urea silane, and silane coupling agents.
The prepreg of the present invention comprises a base material impregnated or coated with the above-stated thermosetting resin composition of the present invention. The prepreg of the present invention is described below in detail.
The prepreg of the present invention can be produced by impregnating or coating a base material with the thermosetting resin composition, which comprises the component (1) or (1)xe2x80x2 and the component (2), and optionally the component (3), then semicuring the resin composition (so as to be in a B-stage) by, for example, heating. As the base material in the present invention, well known ones for use in various laminated sheets for electrically insulating material can be used. Examples of materials for the base material include inorganic fiber, such as E-glass, D-glass, S-glass, and Q-glass, organic fiber, such as polyimide, polyester, and polytetrafluoroethylene, and mixtures thereof. These base materials have forms of, for example, woven fabric, non-woven fabric, roving, chopped strand mat, and surfacing mat, but the material and forms of the base material are appropriately selected depending on the application and performance of a desired shaped product, and, if desired, two or more materials and forms can be used individually or in combination. With respect to the thickness of the base material, there is no particular limitation, and, for example, a base material having a thickness of about 0.03 to 0.5 mm can be used. From the viewpoint of achieving excellent heat resistance and excellent moisture resistance as well as excellent processability, a base material having a surface treated with a silane coupling agent or a base material treated by mechanically splitting is preferred. A base material is impregnated or coated with the resin composition so that the content of the resin in the prepreg dried becomes from 20 to 90% by weight, and then, generally dried by heating at 100 to 200xc2x0 C. for 1 to 30 minutes to semicure the resin composition (so as to be in a B-stage) to obtain the prepreg of the present invention.
Subjecting the above-stated prepreg of the present invention to laminate molding can form the laminated sheet of the present invention. The laminated sheet can be produced by, for example, stacking on one another 1 to 20 pieces of the prepreg of the present invention, placing on one surface or both surfaces of the stacked prepreg a metal foil or metal foils of copper or aluminum, and subjecting the resultant prepreg to laminate molding. With respect to the type of metal foil, there is no particular limitation as long as it can be used in the application of electrically insulating materials. In addition, as conditions for molding, for example, those used in methods for laminated sheet and multilayer sheet for electrically insulating materials can be employed, and, for example, molding can be conducted using a multi-stage press, a multi-stage vacuum press, a continuous molding machine, or an autoclave molding machine by heating at 100 to 250xc2x0 C. at a pressure of 2 to 100 kg/cm2 for 0.1 to 5 hours. Further, the prepreg of the present invention can be combined with a wiring board for inner layer and subjected to laminate molding to produce a multilayer sheet.